Intercellular communication is thought to play an integral role in the complex mechanisms controlling cell determination, differentiation and morphogenesis which result in a higher organism. The proposed study will use the fruitfly, Drosophila melanogaster, to examine changes in the functional properties and biochemical composition of the cell surface through development. The sophisticated genetic methodology available for Drosophila allows the use of a powerful approach not possible in other higher eukaryotes: The systematic recognition of gene mutations that alter cell surface properties, and the analysis of the role of these genetically regulated components in developmental events. The research proposed will focus on changes of the cell surface properties of primordia called imaginal discs. However, since the biochemical characterization of insect cell surface proteins is a novel experimental approach, we had first to develop appropriate protocols for radiolabeling Drosphila proteins and their supsequent analysis. Thus, our initial studies have utilized the most tractable experimental material available: an embryonic cell line. This work indicates that cell surface proteins can be effectively resolved using lactoperoxidase-catalyzed iondinatin and separation by two-dimensional polyacrylamide gel electrophoresis. This method is sufficiently sensitive to detect changes in cell surface protein populations with time during cell proliferation, and in response to the insect hormone ecdysterone. Preliminary experiments with mature wing, leg, and eye-antennal discs show that they share many cell surface proteins, but that some are disc-specific.